The cross section of a copper strip is \(1.0 \mathrm{~mm}\) thick and \(20 \mathrm{~mm}\) wide. There is a 10-A current through this cross section, with the charge carriers traveling down the length of the strip. The strip is placed in a uniform magnetic field that has a magnitude of \(2.0 \mathrm{~T}\) and is directed perpendicular to both the length and the width of the strip. If the number density of free electrons in copper is \(8.47 \times 10^{19} \mathrm{~mm}^{-3}\), calculate \((a)\) the speed of the electrons in the strip and \((b)\) the potential difference across the strip width.